AATCC EP9:2021 pdf download.Evaluation Procedure for Visual Assessment of Color Difference of Textiles
2. Principle
2.1 The color of a specimen or speci- mens and a reference standard are com- pared and evaluated under specific light- ing and viewing conditions. The observed color difference can also be compared with tolerance range specimens.
3. Terminology 3.1 chroma, n.—the proportion of spectrally pure color that expresses the degree of departure from the gray of the same lightness.
3.2 hue, n.—the attribute of visual per- ception according to which a color field is judged similar to one conventionally named yellow, red, blue, or green or a combination of an adjacent pair of these colors, considered to be arranged in a closed ring.
3.3 lightness, n.—the attribute of vi- sual perception by which a non-self-lumi- nous body is judged to reflect more or less light. 3.4 metamerism, n.—visual phenome- non according to which spectrally differ- ent materials have, for a given observer in a given illumination, matching color appearance. The fields may no longer match when viewed in a different light or by a different observer. 3.5 reference standard, n.—a mate- rial that defines the specific color to be matched, and may also be used to define other appearance properties, such as fin- ish, texture and construction. 3.6 tolerance range specimens, n.— selected specimens which deviate from the reference standard in hue, lightness, chroma, or in combinations of the three, and impose a range of observable color differences around the reference standard for evaluation purposes.
5.3.3 Option C. The specimen plane and illumination source shall be parallel to each other and aligned so that the light flux is incident at the center of the speci- men plane, which is set at a 35 ± 5° angle relative to the horizontal. The observer shall view the specimens at a 90° angle, relative to the plane of the specimens. This option shall not be used for evalua- tions of glossy or non-matte specimens. The observer shall take care when evalu- ating specimens not to block the incident light from the source.AATCC EP9 pdf download.